An empirical expression for K-shell ionization cross section by electron impact

An empirical expression is proposed to describe the K-shell ionization cross sections by electron impact over a wide range of atomic numbers (i.e. ) and overvoltages U (i.e. ) defined as being the ratio between the incident electron energy and the ionization energy of the electrons in the K shell. The study is based on the analysis of existing experimental databases for atoms. Agreement is obtained with an accuracy of 10% over the entire atomic number and overvoltage ranges including the near-threshold region. Results are compared with those obtained with other analytical expressions.